It is difficult to make an overall assessment of the degree of metal contamination in estuarine and marine sediments. This is a consequence of variations in analytical procedures between studies and the presence of an unknown natural background in the sediment. Measurement of total (rather than extractable) metal and normalization of concentrations as ratios to an element associated with clays provides a solution to the first difficulty. Expressing these values as enrichment factors relative to pre-industrial sediments from the same environment solves the second.
Levels of anthropogenic enrichment of intertidal sediments in the Humber Estuary have been assessed relative to a baseline provided by sediments deposited in the Humber approximately 5000 years B.P. A sample of consolidated Holocene mud estimated to be at least 100 years old confirmed the appropriateness of this baseline. Normalization relative to Rb, which is not anthropogenically enriched, was the most suitable way to adjust for grain size.
Levels of Ti, Fe, P, V, Cr, Mn, Ni, Cu, Zn, As, Y, Nb and Pb are elevated above this baseline. The most marked enrichments (between 3·5- and 6-fold) are of P, As, Pb, Cu and Zn. Normalized concentrations were spatially rather uniform with two exceptions. A single sample from the north bank showed elevated levels of Pb, Cu, Zn and Cr. An area receiving effluents from an industrialized zone on the south bank, including two titanium dioxide processing factories, showed high levels of a number of elements, particularly Nb. It is suggested that Nb may be a valuable tracer for effluents from the sulphate process of TiO2 extraction.
- chemical pollution
- contaminant measurements
- heavy metals
- titanium dioxide industry